1. Field of the Invention
The invention relates to vehicle wheel end assemblies and in particular to heavy-duty tractor-trailer wheel end assemblies. More particularly, the invention is directed to a heavy duty tractor-trailer wheel end assembly which is internally vented to the vehicle non-drive axle, and in which a filter is incorporated in the axle for preventing migration of contaminants from the interior of the axle to the wheel end assembly thereby preventing premature degradation of the wheel end assembly bearings and/or main seal.
2. Background Art
For many years the heavy-duty tractor-trailer industry has utilized wheel end assemblies which typically are mounted on each end of one or more non-drive axles. Each wheel end assembly typically includes a hub rotatably mounted on a bearing assembly, which in turn is immovably mounted on one of the outboard ends or spindles of the axle. As is well known to those skilled in the art, for normal operation of the wheel end assembly to occur, it must be lubricated with grease or oil and the entire assembly sealed to prevent leakage of the lubricant and also to prevent contaminates from entering the wheel end assembly which could be detrimental to its performance. More specifically, a hubcap is mounted on an outboard end of the hub and a main seal is rotatably mounted on an inboard end of the hub and bearing assembly in abutment with the axle spindle, resulting in a closed or sealed wheel end assembly.
However, during normal operation of a tractor-trailer, heat is generated within the sealed non-drive wheel end assembly due to the friction of the bearings under load. The air or internal atmosphere trapped in the sealed wheel end assembly expands in response to the increased temperature in accordance with well known pressure laws. Moreover, variations in external atmosphere operating conditions such as weather, altitude and temperature can also increase pressure within the sealed wheel end assembly. It follows that if such increased wheel end assembly pressure is not released or reduced, then the main rotating seal of the wheel end assembly is subjected to excessive side loading which leads to premature wear of the seal. Such premature seal wear can in turn result in loss of lubrication from the wheel end assembly and possible premature excessive wear of the bearing assembly.
Heretofore, primarily two methods for managing non-drive wheel end assembly pressure build-up have been utilized. One extensively used prior art method is an external venting system, which vents pressure from the wheel end assembly to the external atmosphere through a port formed usually in the hubcap. The wheel end assembly typically is protected against infiltration of contaminates by a filter element which extends across the open port, or alternatively by a baffle arrangement of open ports. However, it has been found that such an external venting system is not always reliable. More specifically, such a system has been found to allow ingress of water and small particle contaminates into the wheel end assembly, which in turn can adversely affect the life of the bearing assembly and/or main seal. Moreover, it has been found that such external venting systems also can become blocked due to corrosion from road salt or contamination from the external atmosphere, resulting in a build-up of pressure in the wheel end assembly and possible shortening of the life expectancy of the seal.
A second prior art method that often has been used is an internal venting system. More particularly, internal venting systems provide for the flow of expanding gases from the non-drive wheel end assembly into the internal cavity of the hollow non-drive axle, which serves as an accumulator. As is well known in the art and literature, the pressure increase of the expanding gas in the wheel end assembly will be less due to a larger available volume for expansion of the gas into the axle cavity. Since the wheel end assembly remains sealed to the external atmosphere, the bearing assembly and main seal both are protected from external contaminates such as those that plague external venting systems. However, the heavy-duty tractor-trailer industry recently has discovered that debris from the internal surface of the axle can potentially migrate from the axle cavity into the wheel end assembly in an internally vented system. Such contaminant migration can threaten bearing assembly and main seal life in a manner similar to that found in external venting systems.
The present invention solves the problem of migration of contaminates from the axle cavity to the wheel end assembly in an internally vented system by disposing a filter in the axle cavity. The filter effectively blocks the movement of contaminates, but allows air flow between the wheel end assembly and the axle cavity to alleviate pressure build-up in the wheel end assembly, thereby preventing premature wear to the bearing assembly and/or main seal.